Relationships change from baby to adolescent. If you think of birds in the wild, they go from relying on their parents to becoming self sufficient and then finding a mate. Therefore, if you took on the role as "parent" of this bird, it is natural for it to want to make a break from you. That's part of the reason I personally don't think it is necessary or advisable to handraise your own pet bird.
My girl was similar at 3 months and looking back I'm sure it came down to lack of confidence in her surroundings, fear and working out the world around her. These are the ways I changed this behaviour:
1. I worked to build a trust account with her - I stopped forcing her to do things and only did things she was comfortable with
2. I introduced foraging to her diet and then made it the only way she could get her food
3. I did positive reinforcement training to build trust and communication with us.
My girl rarely bites me now. In fact I generally only receive bites during nesting season when she is trying to defend something she sees as a possible nest cavity. Pay a lot of attention to her body language especially when she is around your son. You want to encourage safe interactions between your son and your bird and you don't want your son to become scared of her. You could try getting him to interact with her through her cage bars, perhaps giving her treats, etc. For now, until you are confident that your son and bird know how to interact well together, I think you need to supervise all interactions. I would also recommend you purchase the following DVDs from Barbara Heidenreich: Parrot Behavior
and Training #1, Understanding Parrot Body Language. Both are available from here:
Do you have other birds (especially ringnecks) in your household? What diet is your bird on? What size cage does your bird have? Do you know your bird's fav treats?